Weighting detector configurations in SPECT imaging

ABSTRACT

Method and apparatus for scanning a region of interest (ROI) by a gamma detector. An exemplary method includes determining, for each of multiple detector configurations, a respective weight based on an absorption profile, associating each of a plurality of portions of the ROI with a respective gamma attenuation value; and detecting gamma radiation from multiple detector configurations for time periods allocated among the detector configurations based on the weights determined.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. application Ser. No.16/484,191 filed Aug. 7, 2019, which is the U.S. national phase of PCTApplication No. PCT/IL2018/050129 filed on Feb. 6, 2018, which claimsthe benefit of U.S. Provisional Patent Application No. 62/455,609 filedon Feb. 7, 2017, the disclosures of which are incorporated in theirentireties by reference herein.

FIELD OF THE INVENTION

The present disclosure is in the field of imaging by gamma radiation,and more particularly, but not exclusively, in the field of singlephoton emission computerized tomography (SPECT).

BACKGROUND OF THE INVENTION

In traditional SPECT imaging, a large gamma detector, weighing typicallyabout 500 kg, and having about half a meter in diameter or diagonal, isbrought near a patient for detecting gamma photons emitted from thepatient (who before was injected with a gamma emitting material, alsoknown as radiopharmaceutical). This large and heavy gamma detectorcollects gamma photons for some time, and then moves to anotherposition, for detecting gamma photons from a different side of thepatient's body.

Recently, smaller and lighter gamma detectors have become commerciallyavailable, usually based on Cadmium Zinc Telluride (CZT) crystals.

SUMMARY OF THE INVENTION

Unless otherwise defined, all technical and/or scientific terms usedherein have the same meaning as commonly understood by one of ordinaryskill in the art to which the invention pertains. Although methods andmaterials similar or equivalent to those described herein can be used inthe practice or testing of embodiments of the invention, exemplarymethods and/or materials are described below. In case of conflict, thepatent specification, including definitions, will control. In addition,the materials, methods, and examples are illustrative only and are notintended to be necessarily limiting.

As will be appreciated by one skilled in the art, some embodiments ofthe present invention may be embodied as a system, method or computerprogram product. Accordingly, some embodiments of the present inventionmay take the form of an entirely hardware embodiment, an entirelysoftware embodiment (including firmware, resident software, micro-code,etc.) or an embodiment combining software and hardware aspects that mayall generally be referred to herein as a “circuit,” “module” or“system.” Furthermore, some embodiments of the present invention maytake the form of a computer program product embodied in one or morecomputer readable medium(s) having computer readable program codeembodied thereon. Implementation of the method and/or system of someembodiments of the invention can involve performing and/or completingselected tasks manually, automatically, or a combination thereof.Moreover, according to actual instrumentation and equipment of someembodiments of the method and/or system of the invention, severalselected tasks could be implemented by hardware, by software or byfirmware and/or by a combination thereof, e.g., using an operatingsystem.

For example, hardware for performing selected tasks according to someembodiments of the invention could be implemented as a chip or acircuit. As software, selected tasks according to some embodiments ofthe invention could be implemented as a plurality of softwareinstructions being executed by a computer using any suitable operatingsystem. In an exemplary embodiment of the invention, one or more tasksaccording to some exemplary embodiments of method and/or system asdescribed herein are performed by a data processor, such as a computingplatform for executing a plurality of instructions. Optionally, the dataprocessor includes a volatile memory for storing instructions and/ordata and/or a non-volatile storage, for example, a magnetic hard-diskand/or removable media, for storing instructions and/or data.Optionally, a network connection is provided as well. A display and/or auser input device such as a keyboard or mouse are optionally provided aswell.

Any combination of one or more computer readable medium(s) may beutilized for some embodiments of the invention. The computer readablemedium may be a computer readable signal medium or a computer readablestorage medium. A computer readable storage medium may be, for example,but not limited to, an electronic, magnetic, optical, electromagnetic,infrared, or semiconductor system, apparatus, or device, or any suitablecombination of the foregoing. More specific examples (a non-exhaustivelist) of the computer readable storage medium would include thefollowing: an electrical connection having one or more wires, a portablecomputer diskette, a hard disk, a random access memory (RAM), aread-only memory (ROM), an erasable programmable read-only memory (EPROMor Flash memory), an optical fiber, a portable compact disc read-onlymemory (CD-ROM), an optical storage device, a magnetic storage device,or any suitable combination of the foregoing. In the context of thisdocument, a computer readable storage medium may be any tangible mediumthat can contain, or store a program for use by or in connection with aninstruction execution system, apparatus, or device.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including, but not limited to,electro-magnetic, optical, or any suitable combination thereof. Acomputer readable signal medium may be any computer readable medium thatis not a computer readable storage medium and that can communicate,propagate, or transport a program for use by or in connection with aninstruction execution system, apparatus, or device.

Program code embodied on a computer readable medium and/or data usedthereby may be transmitted using any appropriate medium, including butnot limited to wireless, wireline, optical fiber cable, RF, etc., or anysuitable combination of the foregoing.

Computer program code for carrying out operations for some embodimentsof the present invention may be written in any combination of one ormore programming languages, including an object oriented programminglanguage such as Java, Smalltalk, C++ or the like and conventionalprocedural programming languages, such as the “C” programming languageor similar programming languages. The program code may execute entirelyon the user's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider.

Some embodiments of the present invention may be described below withreference to flowchart illustrations and/or block diagrams of methods,apparatus (systems) and computer program products according toembodiments of the invention. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the flowchart and/or block diagram block orblocks.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other devices to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the flowchart and/or blockdiagram block or blocks. The computer program instructions may also beloaded onto a computer, other programmable data processing apparatus, orother devices to cause a series of operational steps to be performed onthe computer, other programmable apparatus or other devices to produce acomputer implemented process such that the instructions which execute onthe computer or other programmable apparatus provide processes forimplementing the functions/acts specified in the flowchart and/or blockdiagram block or blocks.

Some of the methods described herein are generally designed only for useby a computer, and may not be feasible or practical for performingpurely manually, by a human expert. A human expert who wanted tomanually perform similar tasks, such as measuring dielectric propertiesof a tissue might be expected to use completely different methods, e.g.,making use of expert knowledge and/or the pattern recognitioncapabilities of the human brain, which would be vastly more efficientthan manually going through the steps of the methods described herein.

A broad aspect of some embodiments of the invention includes a method ofscanning, by a gamma detector, a region of interest (ROI). The methodincludes:

determining, for each of multiple detector configurations, a respectiveweight, The weight is determined based on an absorption profile thatassociates each of a plurality of portions of the ROI with a respectivegamma attenuation value. The method further includes detecting gammaradiation from multiple detector configurations for time periodsallocated among the detector configurations based on the weightsdetermined.

In some embodiments, the multiple detector configurations comprise aplurality of configuration sets, wherein a configuration set is a groupof configurations that differ only in one configuration describingparameter.

In some such embodiments, each detector configuration within aconfiguration set is allocated the same period of time, and eachconfiguration set is allocated a time corresponding to the weights.Additionally or alternatively, different detector configurations withina configuration set are allocated different period of times according tothe weights.

Some embodiments include sweeping continuously among multipleconfigurations in a configuration set at sweeping speeds correspondingto the weights.

In some embodiments, each detector configuration within a configurationset is allocated the same period of time, and the number ofconfigurations in the configuration set corresponds to the weights.

In some embodiments, the method includes detecting gamma radiation frommultiple detector configurations based on the weights determinedcomprises devoting more time to detecting gamma radiation with the gammadetector facing the ROI from a direction along which attenuation betweenthe gamma detector and the ROI is higher than to detecting gammaradiation with the gamma detector facing the ROI from a direction alongwhich attenuation between the gamma detector and the ROI is lower.

In some embodiments, the weights are used to determine acquisitiondurations.

In some such embodiments, for each of the multiple detectorconfigurations:

the gamma detector is brought to the detector configuration; and

gamma radiation is detected for the acquisition duration correspondingto the weight determined for the detector configuration.

In some embodiments, the weights are used to determine movement speedsof the detectors.

In some such embodiments, a detector moves continuously among themultiple detector configurations at moving speeds that correspond to theweights.

In some embodiments, at least one detector is swept continuously among afirst plurality of detector configurations at a first sweeping pace, andamong a second plurality of detector configurations at a second sweepingpace.

In some embodiments, a weight determined to a given detectorconfiguration is used to determine a configuration density in thevicinity of the given detector configuration.

In some embodiments, the method includes, for each of the multipledetector configurations:

(a) bringing the gamma detector to the detector configuration;

(b) detecting gamma radiation at the detector configuration;

(c) bringing the gamma detector to a new detector configuration betweenthe detector configuration and another one of the multiple detectorconfigurations;

(d) detecting gamma radiation at the new detector configuration; and

(e) repeating (c) and (d) a number of times, said number being dependenton the weight determined for the detector configuration.

In some embodiments, determining a weight for a specific detectorconfiguration includes estimating a total attenuation from a point inthe ROI to a point in the gamma detector when the gamma detector is inthe specific detector configuration.

In some embodiments, determining a weight for a specific detectorconfiguration includes estimating a total attenuation from each of aplurality of points in the ROI to a corresponding point in the gammadetector when the gamma detector is in the specific detectorconfiguration, and combining the total evaluations estimated for theplurality of points in the ROI to provide the weight.

In some such embodiments, the combining includes summing. In someembodiments, the combining may include finding an order statistic of adistribution of attenuations estimated for all the points in the gammadetector.

In some embodiments, the method also includes generating the absorptionprofile. For example, the absorption profile may be generated based on aCT scan, input from 3D sensors, and/or a SPECT preview scan.

An aspect of some embodiments of the invention includes an apparatus forscanning a region of interest (ROI). The apparatus includes:

a gamma detector controllable to be at multiple detector configurations;and

a processor configured to:

-   -   determine for each of the multiple detector configurations of        the gamma detector a respective weight based on an absorption        profile, the absorption profile comprising an association of        each of a plurality of portions of the ROI with a respective        gamma attenuation value; and    -   control the gamma detector to detect gamma radiation from        multiple detector configurations based on the weights        determined.

In some embodiments, the processor is configured to control the gammadetector to devote more time to detecting gamma radiation with the gammadetector facing the ROI from a direction along which attenuation betweenthe gamma detector and the ROI is higher than to detecting gammaradiation with the gamma detector facing the ROI from a direction alongwhich attenuation between the gamma detector and the ROI is lower.

In some embodiments, the weights correspond to acquisition durations,and the processor is configured to execute the following tasks inrespect to each of multiple detector configurations:

bring the gamma detector to the detector configuration; and

control the gamma detector to detect gamma radiation for the acquisitionduration corresponding to the weight determined for the detectorconfiguration.

In some embodiments, the weights correspond to sweeping paces, and theprocessor is configured to control the gamma detector to sweepcontinuously among multiple detector configurations at paces based onthe weights.

For example, the processor may be configured to control the gammadetector to sweep continuously among a first plurality of detectorconfigurations at a first sweeping pace, and among a second plurality ofdetector configurations at a second sweeping pace.

In some embodiments, the processor is configured to execute thefollowing in respect of each of multiple selected detectorconfigurations:

(a) bring the gamma detector to the selected detector configuration;

(b) control the gamma detector to detect gamma radiation at the selecteddetector configuration;

(c) bring the gamma detector to a non-selected detector configuration,the non-selected detector configuration being in the vicinity of theselected detector configuration;

(d) control the gamma detector to detect gamma radiation at thenon-selected detector configuration; and

(e) repeat (c) and (d) a number of times, each with a differentnon-selected detector configuration in the vicinity of the selecteddetector configuration. The said number of times may be dependent on theweight determined for the selected detector configuration.

In some embodiments, the processor is configured to obtain theabsorption profile from a CT scan.

In some such embodiments, the apparatus also includes a CT scanner, andthe processor is configured to control the CT scanner to scan the ROI;and analyze a resultant scan to obtain the absorption profile.

In some embodiments, the detector configuration includes position of thegamma detector, orientation of the gamma detector, or both position andorientation of the gamma detector.

In some embodiments, the apparatus includes a gantry, and the detectorconfiguration includes a gantry angle.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are herein described, by way ofexample only, with reference to the accompanying drawings. With specificreference now to the drawings in detail, it is stressed that theparticulars shown are by way of example and for purposes of illustrativediscussion of embodiments of the invention. In this regard, thedescription taken with the drawings makes apparent to those skilled inthe art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1A and FIG. 1B are diagrammatic illustrations of a region ofinterest being a part of a body part, as viewed by a gamma detector fromdifferent detector configurations;

FIG. 2 is a flowchart of a method for scanning a region of interest(ROI), by a gamma detector according to some embodiments of theinvention;

FIG. 3A is an exemplary attenuation profile;

FIG. 3B is a graph showing the weights assigned to different swivelangles according to some embodiments of the invention;

FIG. 3C is another exemplary attenuation profile;

FIG. 3D is a graph showing the weights assigned to different swivelangles according to some embodiments of the invention;

FIG. 4A is a flowchart of an exemplary method for determining a weightfor a specific detector configuration according to some embodiments ofthe invention;

FIG. 4B is a diagrammatic illustration of a gamma detector;

FIG. 5A is a reproduction of a SPECT scan of a head phantom;

FIG. 5B is a reproduction of a SPECT scan of the same head phantom shownin FIG. 5A, scanned according to some embodiments of the invention;

FIG. 6A is a diagrammatic presentation of an apparatus for scanning aregion of interest (ROI) according to some embodiments of the invention;

FIG. 6B is a diagrammatic presentation of a processor according to someembodiments of the invention;

FIG. 7A is a cross-sectional illustration of a gamma detector accordingto some embodiments of the invention; and

FIG. 7B is an illustration of a different cross-section in the gammadetector shown in FIG. 7A.

DETAILED DESCRIPTION

An aspect of some embodiments of the invention includes a method ofscanning a region of interest in a patient. The region of interest maybe, any organ, tissue, or organ part, or body region. For example, thepatient's brain, a certain part inside the brain (e.g., the basalganglia), the patient's liver, kidney, spine, bones, thyroid,parathyroid, lungs, lymphatic system, etc. While the clinicallyinteresting region (also referred to herein as region of interest, orROI) may be relatively small, the region scanned in practice may belarger. Scanning a larger region has two main benefits: providing acontext to the image of the region of interest, and reducing artifacts.Ideally, every emitter within the patient's body is scanned from everypossible angle.

While in many cases the scanning is carried out by multiple gammadetectors at the same time (e.g., 4, 6, 8, 12 detectors, or intermediatenumber), the present disclosure refers to a single detector, under theunderstanding that the same principles may apply to operating each oneof the detectors.

The gamma detector may have several configurations. A configuration ofthe gamma detector may define the spatial relation between the detectorand the body of the patient. The spatial relationship may be defined byone or more configuration describing parameters. For example, in someembodiments, the gamma detector is mounted on an extendable arm, thatcan extend towards and away of the patient. The distance from thepatient may form part of the gamma detector configuration and may beconsidered a configuration describing parameter. Similarly, the extentto which the extendable arm is extended may form part of the gammadetector configuration and may be considered a configuration describingparameter. In some embodiments, the extendable arm is supported on agantry that may be rotated around the patient to various angles. Thegantry angle may form part of the gamma detector configuration and maybe considered a configuration describing parameter. In some embodiments,even in the absence of a revolving gantry, the gamma detector may bepositioned in different angles in respect to the patient, e.g., facingthe nose, facing the left ear, etc. In some embodiments, these facingangles may form part of the gamma detector configuration and may beconsidered a configuration describing parameter. In some embodiments,the gamma detector is mounted on the extendable arm so the detector canswivel with respect to the arm. The swivel angle may also form a part ofthe detector configuration. In some embodiments, the gamma detectorconfiguration may be represented by a vector, the different componentsof which represent different configuration describing parameters, forexample, gantry angle, swivel angle, distance from the patient, etc.

In some embodiments, detector configurations that differ in only oneconfiguration describing parameter (e.g., differ only in swivel angle)are considered as a set of detector configurations, also referred hereinas a configuration set. For example, in some embodiments, aconfiguration set includes a group of detector configurations having acommon distance from the patient and gantry angle, and differ only inswivel angle. In some embodiments, the configuration set includes allthe detector configurations that differ in only one configurationdescribing parameter.

In some embodiments, the region of interest may be scanned by each gammadetector from multiple detector configurations. For example, one gammadetector may be used for some time period at a certain gantry angle andswivel angle, and then swivel to another swivel angle for another timeperiod. An aspect of some embodiments of the invention includes methodsfor allocating scanning time between detector configurations. Forexample, a scan carried out with equal time periods allocated to alldetector configurations, may result in varying image quality, where theouter parts of the imaged body part are reconstructed with higher imagequality compared to the inner parts. The inventors suggested that thiseffect has to do with attenuation of the gamma radiation on its way fromthe inner parts to the detector, which was more significant than theattenuation of the gamma radiation on its way from the outer parts tothe gamma detector.

Thus, a region of interest may have “hidden” regions, and “visible”regions. A region may be considered “visible” if gamma radiation emittedfrom the region goes under only minimal attenuation on its way to thedetector. A region may be considered “hidden” if gamma radiation emittedfrom the region goes under significant attenuation on its way to thedetector. More specifically, the “visibility” depends on the total gammaattenuation along the path between the photon emission sight and thedetector. As apparent from these definitions, being “visible” or“hidden” is not an intrinsic property of the emitting site, but dependsalso on the location of the detector and the attenuating media.

The concepts of hidden and visible regions are illustrated in FIGS. 1Aand 1B, which are diagrammatic illustrations of a body part 10 havingtherein a region of interest 12, scanned by detector 14 at twoconfigurations: configuration A in FIG. 1A and configuration B at FIG.1B. Assuming that body part 10 is homogeneous, one can see that inrespect to configuration A (i.e., in FIG. 1A), ROI 12 has a very visibleportion X, and a portion Y of very high hiddenness. In respect toconfiguration B (i.e., in FIG. 1B), both portions X and Y are out of thefield of view of the detector. However, if the detector may swivel toface these portions (e.g., in respect to point 16, as shown by thearrow), then, when directly facing the detector, portions X and Y aresimilarly visible, at some intermediate level between the visibilitylevel of X and Y in respect to configuration A.

To cope with the problem that more hidden regions are imaged at lowerquality under equal allocation of scanning time between detectorconfigurations, the inventors suggested spending more of the scanningtime at configurations where the ROI is hidden then at configurationswhere the ROI is visible. The visibility of an ROI as viewed by adetector at a specified configuration may be estimated by variousmethods, some of which are described below, from an absorption profileof the ROI at the specified configuration. The absorption profile mayalso include data on body portions out of the ROI, particularly thoseresiding within the photon travel path, such as spot Z.

Looking at FIG. 1A and FIG. 1B from another perspective, every detectorconfiguration has its own visible spots and hidden spots. For example,in configuration A, spot X is the most visible, then Z and then Y; andin configuration B, spot Z is most visible then spots X and Y. So foreach spot, each detector configuration may have a different “visibility”value.

Since spot Z is out of the ROI, its degree of visibility may beirrelevant for allocating scanning time, at least in some embodiments.It may also happen that spots X and Y are out of the field of view ofdetector 14 when in configuration B, so they may be irrelevant forallocating scanning time to configuration A, at least in someembodiments. Thus, in some embodiments, to allocate scanning timebetween configurations A and B, the visibility of parts X, W, and Z, inrespect of configuration B are taken into account, and the visibility ofpart W in respect to configuration A is taken into account.

Quantitatively, the degree of visibility of a point in respect to aspecific detector configuration may be represented by a gammaattenuation value, indicating the attenuation of gamma radiation on itsway to the detector from the point. The gamma attenuation valuesassigned to ROI points within the field of view of the detector at agiven configuration may then be combined for a single weight associatedwith the given detector configuration. This weight may be taken intoconsideration in allocating the scanning time among the detectorconfigurations.

Thus, a scanning method according to some embodiments of the presentinvention includes determining, for each of multiple detectorconfigurations, a respective weight based on an absorption profileassociating each of a plurality of portions of the ROI with a respectivegamma attenuation value; and

detecting gamma radiation from multiple detector configurations for timeperiods allocated among the detector configurations based on the weightsdetermined.

In some embodiments, the time periods are so allocated, that timeallocated to scan hidden portions of the ROI is larger than timeallocation to scan visible portions of the ROI.

In some embodiments, the weights correspond to acquisition durations.For example, for each of multiple specific detector configurationstaking part in the scanning, the gamma detector may be first brought tothe configuration, and then detect gamma radiation for an acquisitionduration corresponding to the weight determined for the specificdetector configuration. As used herein, two quantities, A and Bcorrespond to each other if each A has a matching B, and similar As havematching Bs that are similar to each other. In some embodiments,correspondence may take the form of a linear equation (e.g., B=pA+q), orother monotonous and differentiable equation (e.g., B=1/A) that allowsdetermining B for a given A. In some embodiments, values are similar ifthey differ from each other by 10% or less of the larger one.

In some embodiments, the weights correspond to motion speeds. Forexample, in some such embodiments, the scanning may include movingcontinuously among multiple detector configurations at differing motionspeeds. In some embodiments, movement over a first group of detectorconfigurations may be at a first single, constant, pace, and moving overa second group of detector configurations may be at a second single,constant, pace, different than the first. In some embodiments, the twogroups of detector configurations are swept continuously; in someembodiments, there is an intermission between the sweeping of the twogroups.

In some embodiments, the weights may correspond to a configurationdensity in the vicinity of the detector configuration. For example,detection may take place at many configurations that differ onlyslightly from one another (e.g., in swivel angle) when looking at ahidden region, and at fewer configurations, that differ moresignificantly from each other (e.g., in the swivel angle), when lookingat a visible region. In some such embodiments, the time spent at eachconfiguration is the same.

In some embodiments, assigning the same weight to all the configurationswithin a configuration set results in each configuration being allocatedthe same time and the configuration density being uniform. Equal weightsin embodiments where the detectors move continuously along theconfigurations may result in constant movement speed.

In some embodiments, assigning different weights to differentconfigurations in a configuration set results in assigning differentacquisition times to the different configurations. The configurationdensity in the set may be uniform (e.g., the swivel angel may change bya constant amount from one configuration to the following one in theset).

In some embodiments, assigning different weights to differentconfigurations in a configuration set results in different configurationdensity. For example, if a first configuration (say, of swivelangle=30°) has a higher weight than a second configuration (say, ofswivel angle=60°), detection may take place at more configurationsaround the first (e.g., at 36°, 33°, 27°, and 24°) than around thesecond (e.g., 55° and 65°). In some such embodiments, the acquisitiontimes allotted to each configuration may be the same.

In some embodiments, the detector sweeps across various configurationscontinuously, and assigning larger weight to a certain configuration ina configuration set may cause the detector to go more slowly around thisconfiguration, while assigning a smaller weight cause the detector to gomore swiftly around this configuration.

It is to be understood that in some embodiments, higher weight may causepaying more time, density, or slowness, while in other embodiments,higher weights may cause paying less time, density, or slowness.However, in all embodiments, higher absorption (i.e., lower visibility)is connected through the weights to longer acquisition times, higherconfiguration density, or slower movement.

Before explaining at least one embodiment of the invention in detail, itis to be understood that the invention is not necessarily limited in itsapplication to the details of construction and the arrangement of thecomponents and/or methods set forth in the following description and/orillustrated in the drawings and/or the Examples. The invention iscapable of other embodiments or of being practiced or carried out invarious ways.

FIG. 2 is a flowchart of a method 200 for scanning a region of interest(ROI), by a gamma detector. Method 200 includes two main parts:associating each detector configuration with a weight; and detectinggamma radiation from multiple detector configurations based on theseweights.

For example, method 200 may include a step 202 of determining arespective weight for each of multiple detector configurations. Theweights may be determined based on an absorption profile of the ROI. Theabsorption profile may include a representation of the ROI divided intoportions. In some embodiments, the portions may overlap with oneanother. In some embodiments, the portions are mutually exclusive. Insome embodiments, the totality of the portions covers each and every bitof the region of interest. In some embodiments, the totality of theportions covers the ROI only partially. The absorption profile may alsoinclude an association between each of the portions and a respectivegamma attenuation value. In some embodiments, some or all of the gammaattenuation values may be the same, but in many embodiments, at leasttwo different gamma attenuation values are associated with differentportions, one value with each portion.

FIGS. 3A and 3C, described below, are examples of attenuation profile.FIG. 4A, described further below, is a flowchart of an exemplary method400 for determining a weight for a specific detector configuration.

Without going into the details of any specific attenuation profile ormethod for determining weights, it may be explained that each weight isassociated with a given portion of the ROI based on the visibility ofthat portion. For example, the weight may be based on the percentage ofthe gamma photons expected to be detected by the detector at thespecific detector configuration, out of the total number of photonsexpected to emerge from the given portion of the ROI towards thedetector. In some embodiments, it may be assumed that each photonemerging towards the detector is either detected by the detector orattenuated on the way to the detector. Accordingly, in some embodiments,the weight may be based on the percentage of the photons expected to beattenuated on their way to the detector. In some embodiments, theweights are indicative of the above-mentioned percentages. For example,the weights may be equal to a percentage described above, or be afunction (e.g., injective function) thereof.

Method 200 may further include a step 204, of detecting gamma radiationfrom multiple detector configurations for time periods allocated amongthe detector configurations based on the weights determined. Withoutgoing into the details of any such specific method, it may be explainedthat in some embodiments, step 204 includes devoting more time todetecting gamma radiation with the detector in a configuration whereinthe ROI is hidden from the detector, than in a configuration wherein theROI is visible to the detector. For example, step 204 may includedevoting more time to detecting gamma radiation with the gamma detectorfacing the ROI from a direction along which attenuation between thegamma detector and the ROI is higher (e.g., higher than a predeterminedthreshold) than to detecting gamma radiation with the gamma detectorfacing the ROI from a direction along which attenuation between thegamma detector and the ROI is lower (e.g., lower than the predeterminedthreshold). In some embodiments, there is no need to determine athreshold, and step 204 may include devoting a first time duration todetecting gamma radiation with the gamma detector facing the ROI from adirection along which attenuation between the gamma detector and the ROIhas a first attenuation value and devoting a second time duration todetecting gamma radiation with the gamma detector facing the ROI from adirection along which attenuation between the gamma detector and the ROIhas a second attenuation value, so that the second time duration islonger than the first time duration if the first attenuation value ishigher than the second attenuation value.

This way, the visibility of the ROI to the detector at differentconfigurations may be factored out, so that each detector configurationcontributes to the scanning process a similar amount of detectedphotons, regardless of the visibility of the ROI to the detector atdifferent detector configurations. In some embodiments, the final imageobtained by scanning method 200 is not influenced by the visibility ofdifferent portions of the ROI to detectors at different configurations,and all portions, visible and hidden alike, are imaged at similarquality. The visibility of a portion of the ROI may be defined as anaverage over the visibility of that portion to different detectorconfigurations. In some embodiments, the final image obtained byscanning method 200 is influenced by the visibility of differentportions, but less than if scanning times are allocated to detectorconfigurations regardless of the visibility of the ROI to the detectorat these detector configurations. For example, the phenomenon that morehidden regions are scanned at lower quality than visible regions maymaintain, but be less severe than if time is allocated to detectorconfiguration regardless of the visibility of the region of interest toa detector in different configurations. In some embodiments, the finalimage obtained by scanning method 200 is influenced by the visibility ofdifferent portions, so that hidden portions are imaged at higher qualitythan visible portions.

FIG. 5A is a SPECT scan of a head phantom, scanned with allocatingscanning time to different detector configurations regardless ofdifferences in the visibility of different portions of the brain (whichwas the region of interest) to the detector. FIG. 5B is a SPECT scan ofthe same head phantom, scanned for the same total scanning time, butwith scanning time allocated to different detector configurations basedon the visibility of the center of the brain to the detector. It may beseen that in FIG. 5B the center of the brain is imaged in higher qualitythan in FIG. 5A. The total scanning time for producing the scans shownin FIGS. 5A and 5B were the same.

FIG. 3A is an exemplary attenuation profile 300. Attenuation profile 300comprises an image showing a low-resolution slice of a CT scan of ahuman chest. Some parts easily recognizable in the figure are the lungs,heart, and spine. In some embodiments, the region of interest may bedefined by the outline of the chest, marked 302. The shading ofdifferent tissues in the figure is indicative of the attenuationcoefficient of the respective tissues for the X-rays used for generatingthe image. The darker is a portion of the image, the lower is its X-rayattenuation, and the attenuation at the darkest parts, outside outline302, is practically zero. As there is a straightforward transformationfrom attenuation of X-rays to attenuation of gamma radiation, theshading is also indicative of the gamma attenuation of the respectivetissues.

FIG. 3B is an exemplary graph associating weights to swivel angles basedon attenuation profile 300, for a configuration set at which thedetector is at position 304. In some embodiments, the configuration setdetermines the distance of the detector from chest 300 by a degree ofextension of an extendible arm carrying the detector (e.g., arm 1116 inFIG. 6A). In some embodiments, the configuration set determines theposition of the detector, i.e., below the center of the chest, by agantry angle (e.g., ϕ in FIG. 6A). The configuration set also includes aswivel angle (see arrow 1620 in FIG. 7A). In the exemplary graph shownin FIG. 3B the weight is determined for each swivel angle by integratingthe attenuation coefficient along a line emerging from the detector'sposition 302 and directed according to the swivel angle to obtain anintegrated attenuation. In the example shown, the weight is exponent ofthe integrated attenuation. In some embodiments, the weight may be theintegrated attenuation, or any value derivable straightforwardly fromthe integrated attenuation or from the exponent of the integratedattenuation.

FIG. 3A includes two lines at about 70° and at about 100° (measuredclockwise from horizontal line 306, and marked 310 and 311respectively), and FIG. 3B includes two vertical dashed lines at thecorresponding angles, marked with the same respective numerals. As canbe seen, the maximum of the attenuation is along a line going throughthe middle of the heart, while lines going through the lungs (e.g., theline emerging at an angle of about 70°) have a smaller weight. In someembodiments, running a SPECT scan based on the weights shown in FIG. 3Bresults in spending no acquisition time at angles smaller than 30° orlarger than 150°, while spending most of the time at angles between 80°and 120°. Spending more time detecting gamma radiation while facingregions of high attenuation may compensate for the relatively smallamount of radiation emerging from these regions per second, so that thenumber of photons (or the amount of radiation) detected from any part ofthe ROI is substantially the same.

FIG. 3C is another exemplary attenuation profile, that includes anoutline of an ROI, marked 302. The outline may be obtained, for example,by interpolating between positions of a plurality (e.g., 6 or 8) ofdetectors when they nearly touch the patient's body. In the attenuationprofile of FIG. 3C, the entire area defined by outline 302 attenuatesuniformly. This may be, for example, an approximation to an attenuationprofile of a body part that includes only tissues of similarattenuation, such as muscle, fat, and bones. Like numerals used in FIGS.3A and 3C refer to like parts.

FIG. 3D is an exemplary graph associating weights to swivel angles basedon the attenuation profile of FIG. 3C. In the exemplary graph shown inFIG. 3D the weight is determined for each swivel angle by multiplyingthe attenuation coefficient of the ROI by a length of a line emergingfrom the detector's position 302 and directed according to the swivelangle.

FIG. 3C includes two lines at about 45° and at about 75° (measuredclockwise from horizontal line 306, and marked 310 and 311,respectively), and FIG. 3D includes two vertical dashed lines at thecorresponding angles, marked with the same numerals. As can be seen, themaximum of the attenuation is between about 60° and about 120°. In someembodiments, running a SPECT scan based on the weights shown in FIG. 3Dresults in spending no acquisition time at angles smaller than 45° orlarger than 135°, while spending time mainly at angles between 80° and120°.

FIG. 4A is a flowchart of an exemplary method 400 for determining aweight for a specific detector configuration based on an attenuationprofile. Method 400 may include two main steps: step 402 includesdetermining an ROI visibility value for the detector configuration; andstep 404 of determining the weight based on the visibility value.

To show how a visibility value may be determined for a detectorconfiguration reference is made to FIG. 4B. In FIG. 4B a detector 420 isshown to include a parallel holes collimator 422, and a detectingcrystal 424. The probability that photons emerging from a pixel 430directly towards hole 432 in collimator 422 through ROI edge 440, areattenuated before reaching detecting crystal 424 may be given byequation (1):

$\begin{matrix}{P = e^{- {\int_{R_{1}}^{R_{2}}{{\mu(l)}dl}}}} & (1)\end{matrix}$Wherein P is the probability that a photon is attenuated, R₁ is ROI edge440, R₂ is voxel 430, and μ(l) is the linear attenuation of the gammaphotons in the ROI as a function of the location along a path going fromvoxel 430 to ROI edge 440. If the linear attenuation has a constantvalue along that path (or across the entire ROI, as illustrated in FIG.3C), equation (1) may take a simpler form, given in equation (2)P=e ^(−μ) ⁰ ^(Δl)  (2)Wherein μ₀ is the constant value of the linear attenuation, and Δl isthe length of the path going from voxel 430 to ROI edge 440.In both cases, the probability that the photon is detected is given byequation (3)P _(reaching the collimaor)=1−P  (2)

If the photon emerges in a different direction, it finds a septum on itsway to detection crystal 424, and for the purpose of the presentdiscussion is assumed to be 100% absorbed by the septum. So theprobability of being detected of all photons that do not emerge directlyinto one of the holes is 0. In some embodiments, the probability to beabsorbed by a septum is given a more precise (non-zero) value, and takeninto account.

In some embodiments, a weight for a specific detector configuration isdetermined based on an estimation of a total attenuation from a point inthe ROI (e.g., point 430) to a point in the gamma detector (e.g., point450, which is in line with points 430 and 440, and makes part ofdetection crystal 424). In a similar way, a probability may becalculated for photons emerging in any direction from each and everyvoxel in the region of interest being detected by any point in the gammadetector.

These probabilities may be combined to generate a weight. In someembodiments, the combination may be based on summing. For example, insome embodiments, the visibility of the ROI to the detector in the givendetector configuration may be defined as the sum of the probability ofbeing detected of photons emerging from each and every voxel in theregion of interest in any available direction. In some embodiments, thesum is not over each and every voxel, but over some selected voxels. Insome embodiments, the probability to be detected despite of goingthrough one or more septa of collimator 422 is taken into account moreaccurately than in the above-described process, where it was assumed tobe 0. In some embodiments, not all the directions along which photonsmay emerge are taken into account, but only some of the directions. Whenonly some voxels are considered, the combination may include summation,for example weighted summation. For example, each voxel considered maybe taken to represent a number of voxels, and may be weighted by thisnumber.

In some embodiments, a probability distribution is calculated. Theprobability distribution may include probabilities to detect photons bydifferent points across detection crystal 424. For example, in themulti-hole collimator illustrated in FIG. 4B, the probabilitydistribution may include a separate probability to detect photons foreach detector cell corresponding to one of the holes. In some suchembodiments, the weight is determined as an order statistic of thisdistribution (e.g., the maximum, median, etc.)

Once a visibility value is determined for the detector configuration,for example, in any of the manners described above, a weight for thedetector configuration may be calculated based on it. For example, insome embodiments, the weight associated with a detector configurationmay be the visibility value determined for that detector configuration.In some embodiments, the weight may be indicative of the visibilityvalue, for example, the visibility value multiplied by some factor,which may be equal for all the detector configurations or may differbetween detector configurations. For example, the factor may bedifferent for detector configurations facing regions of different levelsof importance. For example, if some portion of the ROI is of specialinterest, and there is a need to image it with a higher quality, thefactor multiplying the visibility value of detector configurationsfacing the region of special interest may be higher than a factordoubling the visibility value of detector configuration that do not facethe region of special interest.

As mentioned above, in some embodiments, acquisition time periods may beallocated among the detector configurations based on the weightsdetermined. In some embodiments this is done by dividing a totalacquisition time among a number of discrete configurations, andallocating to each detector configuration a time period proportional toits weight. The proportionality factor may be determined by firstdetermining a target scanning time, and then dividing the targetscanning time by a sum of the weights associated with all the detectorconfigurations. In such examples, the weights correspond to acquisitiondurations.

For example, in some embodiments, multiple detector configurations(e.g., first, second, third, etc.) are determined to be used for thescanning before scanning begins. Then, the gamma detector is brought tothe first configuration, and gamma radiation is detected for a timeperiod corresponding to the weight determined for the firstconfiguration. When that time period ends, the detector is brought tothe second configuration, and gamma radiation is detected for a timeperiod corresponding to the weight determined for the secondconfiguration, and so on, until detection has been carried out from eachof the multiple detector configurations.

In some embodiments, the weights may be used to determine sweepingpaces. The sweeping may be of the detector along differentconfigurations. In some such embodiments, the detector moves fluentlyfrom one configuration to the other in pace that may be controlled andchanged during detection. The sweeping pace may be determined by theweights. For example, consider a case where detection is to be carriedout at all swiveling angles between 30° and 150°, and weights have beendetermined only to some these endless number of swiveling angles, e.g.,swiveling angles of 30°, 60°, 90°, 120°, and 150°. The detector may beswiveled fluently between 30° and 150°, and the swivel pace may changeduring swiveling based on the weights determined for the differentswivel angles. For example, in some embodiments, the swivel pace between30°, and 60° may correspond to the weight determined for 30°; the swivelpace between 60°, and 90° may correspond to the weight determined for60°, etc. In some embodiments, the swivel pace between 30° and 90° maycorrespond to the weight determined for 60°; and the swivel pace between90° and 150° may correspond to the weight determined for 120°. In someembodiments, the swivel pace between 30°, and 60° may correspond to anaverage of the weight determined for 30° and the weight determined for60°, etc.

More generally, sweep paces may be determined based on weightsdetermined for configurations within the sweep and/or configurationsbetween which the sweeps occur. In some embodiments, the sweeping stopsbefore sweeping pace is changed, so the sweep is made of a plurality ofdiscrete sweeps, each of which being fluent by its own. In someembodiments, there is no stop, and the sweep is continuous.

In some embodiments, the weight associated with a detector configurationmay be used to determine a configuration density in the vicinity of thedetector configuration. For example, in some embodiments, higher weightcorresponds to higher configuration density. For example, the detectormay spend the same time duration at each configuration, but stays atmore configurations in the vicinity of a configuration associated withhigher weight than in the vicinity of a configuration associated withlower weight.

The vicinity of a configuration may be determined, in some embodiments,based on distances in a configuration space. The configuration space maybe one-dimensional, e.g., when only one configuration defining parameter(e.g., swivel angel or gantry position) is changed. The configurationspace may be multi-dimensional, in which case the vicinity may bedefined based on the distance between the configurations in amulti-dimensional space. The vicinity may be defined as a certaindistance, and the number of configurations used for scanning within asphere having a radius (or diameter) of the certain distance may bedetermined according to a weight determined for a configuration at thecenter of the sphere. In some embodiments, different distances may bedetermined along different configuration defining parameters, forexample, a non-selected configuration may be considered in the vicinityof a selected configuration if the two are within a certain distance inswivel angle (e.g., 20°) and a certain (possibly different) distance ingantry angle (e.g., 10°).

FIG. 6A is a diagrammatic presentation of an exemplary apparatus 1100for scanning a region of interest (ROI). Apparatus 1100 includes asupport (1102), a gantry (1104), 4 3D sensors 1106, and a processor(1108).

Support 1102 is configured to support patient 1110 during imaging. Thepatient support may be configured to support lying patients, asillustrated. In some embodiments, the patient support may be configuredto support standing patients, sitting patients, and/or leaning patients.For example, the support may be horizontal, such as a patient bed,vertical, such as a wall or a back of a chair and the like. The supportmay be made of low attenuation material, for refraining from attenuatinggamma radiation emanating from the patient towards the detectors on theother side of the support.

Gantry 1104 includes a cylindrical frame that supports multiple gammadetectors 1112. In some embodiments, each gamma detector faces support102. An example of a gamma detector is described below in relation toFIG. 7A and FIG. 7B. Each detection head 1112 may be mounted on anextendable arm 1116, configured to take the detection head mounted on itin a linear in-out movement, so as to bring the detector closer to thepatient or away of it. Gantry 1104 is rotatable around an axis, along,for example, angle ϕ, to allow the gamma detectors to rotate around thesupport.

Each detection head 1112 may include a semiconductor detecting crystal,for example cadmium zinc telluride (CZT) detecting crystal. A linearactuator is provided to linearly maneuver extendable arm 1116 so thatdetection head 1112 moves toward and from patient support 1102.Optionally, the linear actuator is mechanical actuator that convertsrotary motion of a control knob into linear displacement, a hydraulicactuator or hydraulic cylinder, for example a hollow cylinder having apiston, a piezoelectric actuator having a voltage dependent expandableunit, and/or an electro-mechanical actuator that is based on an electricmotor, such a stepper motor and the like. In some embodiments, thelinear actuator may include a stepper motor and a sensor, optionally amagnetic sensor (e.g., encoder) that senses the actual position ofdetection head 1112, to provide feedback on the control of the steppermotor. The control of each linear actuator may be performed according toa scanning plan. In some embodiments, the scanning plan may be generatedby processor 1108. In some embodiments, the scanning plan may begenerated outside apparatus 1100, and imported to the processor.Regardless of the origin of the plan, processor 1108 may control otherparts of the apparatus to carry out the plan. The scanning plan mayinclude, for example, a list of detector configurations for each of thedetectors, and a time to dwell at each configuration. A configurationmay be defined, for example, by angle of gantry 1104, the extension ofextendable arm 1116, and a swiveling angle of the detection head 1112.

Each sensor 1106 is a 3D sensor arranged to sense a portion of patient1110 when the patient is supported by support 1102. These optionalsensors may provide data to delimit the region of interest, and thisdata may be used in generating an attenuation profile, for example,having an attenuation of water in the region of interest, and of air outof the patient, for example, as described in FIG. 3C herein. Each sensor1106 may be, for example, optical, ultrasonic, or based on radio wavesor microwaves. Examples of specific technologies used in such sensorsare structured light sensors, illumination assisted stereo sensors,passive stereo sensors, radar sensors, Lidar sensors, and time of flightsensors. Commercially available embodiments of such sensors includeMicrosoft Kinect, Intel RealSense Camera F200, Mantis Vision's 3Dscanners, PMD technologies PicoFlexx, and Vayyar Imaging Walabot. Sensor1106 is configured to output signals indicative of 3D coordinates ofpoints (e.g., point 1114, 1114′) on an outer surface of patient 1110and/or support 1102. In some embodiments, the 3D sensor(s) provides apoint cloud that allows approximating the outer surface of the bedand/or patient. In some embodiments, the 3D sensor may be installed onthe gantry, as shown in FIG. 6 . Alternatively or additionally, one ormore 3D sensors may be installed on the extendable arm 1116, insidedetection head 1112, on a separate support structure, or at any otherlocation, at which the one or more 3D sensors can sense the position ofat least one point of the outer surface of the patient and/or support.

Processor 1108 may be configured to determine for each of detectorconfiguration, a respective weight; and allocate among the detectorconfigurations time periods based on the determined weights, therebygenerating a scanning plan. Processor 1108 may be further configured tocontrol other parts of the apparatus to scan according to the scanningplan generated, for example, the processor may control gantry 1104,extendable arms 1116, and the swivel angle of the detector in each ofthe detection heads 1112, so that gamma radiation is detected by eachgamma detector at each detector configuration for the time periodallocated to the respective detector configuration. The determination ofthe weights by processor 1108 may be based on an absorption profile,associating each of a plurality of portions of the ROI with a respectivegamma attenuation value, for example, an absorption profile of the kindillustrated in FIG. 3A. Processor 1108 may be configured to control thedetectors concertedly, for example, to avoid interference between thedetectors, and to use each of the detectors for scanning a differentportion of the ROI, so that the detectors together scan the entire ROIin less time than it would have been scanned by a single detector.Nevertheless, the invention is not limited to any number of detectors,and in some embodiments, a single detector may do.

As used herein, if a machine (e.g., a processor) is described as“configured to” perform a particular task (e.g., determine weights),then the machine includes components, parts, or aspects (e.g., software)that enable the machine to perform the particular task. In someembodiments, the machine may perform this task during operation.Processor 1108 is diagrammatically described in FIG. 6B. Processor 1108may include an input 1202 configured to receive from 3D sensor 1106 dataindicative of at least one surface point 114. The data received from theprocessor may be raw data, convertible to 3D coordinates of the one ormore surface points by processor 1108 or any processing module connectedto processor 1108. In some embodiments, the 3D sensors may send thecoordinates directly to processor 1108. Data indicative of the 3Dcoordinates of the one or more surface points may be stored in memory1204, and may be used by processor 1108 to generate an absorptionprofile of the kind illustrated in FIG. 3B, for example, to generate theouter shape of the ROI (see curve 302) based on the input from the 3Dsensors, and attribute to all points within the curve a predeterminedattenuation value. The predetermined attenuation value may bepre-programmed into processor 1108, and stored, for example, on memory1204, further described below. In some embodiments, input 1202 may beconfigured to receive a scan (e.g., a CT scan) of the region of interestand different values of linear attenuation parameters associated withdifferent portions of the scanned ROI, for example, as described in thecontext of FIG. 3A. The scan may be taken by a scanner integrated withapparatus 1100 into a dual modality scanner. The absorption profile(regardless what data it is based on), may be stored on memory 1204. Insome embodiments, the detectors may be brought as close as possible tothe patient around the ROI, and the outline of the ROI may be determinedbased on the location of the detectors. The volume within the outlinemay be assumed to absorb in a certain manner (e.g., uniformly as ifcompletely filled with water, or one part as water and another part as apatient bed, etc.). The absorption profile may be calculated based onthe volume outline and its assumed absorption, and stored on memory1024.

Processor 1108 may further include a memory 1206 storing instructionsfor determining weights based on input received through input 1202.Memory 1206 may be separate from memory 1204, or may make part of memory1204. An example of a method by which processor 1108 may determine theweights is described in FIG. 4A. Processor 1108 may further include acentral processing unit (CPU) 1208 configured to carry out theinstructions saved on memory 1206 using data stored on memory 1204 andsend results of the processing to output 1210.

Output 1210 may be connected to a motor (not shown) moving gantry 1104,to motors moving extendable arms 1116, and to motors moving thedetectors inside the detection heads to the appropriate swivel angles,in accordance to the weights determined to the various detectorconfigurations based on data received through input 1202 andinstructions stored on memory 1206.

System 1100 may also include a user interface 1214. User interface 1214may allow the user (for example, a technologist) to indicate a kind ofscan to be performed. The user interface may include, for example, abarcode reader to read a barcode attached to an imaging request for thepatient. Optionally or alternatively, the user interface may include akeyboard, touchscreen, or any other input device allowing the user toindicate the kind of scan required. In some embodiments, user interface1214 may be configured to allow a user to manually indicate a portion ofthe ROI where high image quality is most desired. For example, userinterface 1214 may include a display for displaying an image of the ROI.The image may be, for example, a SPECT preview scan or an image takenwith a different modality (e.g., a CT scan, MR image, ultrasound image).The displayed image may show the ROI at low quality, a scan taken at adifferent occasion (e.g., a few months before), etc. The display mayinclude a touchscreen, mouse, or any other arrangement allowing a userto point to a certain region in the displayed image. Once an indicationhas been received, that a certain region is to be imaged at higherquality than others, this may be taken into consideration in assigningweights to detector configurations. For example, higher weights may beassigned to detector configurations that the indicated region is withintheir field of view.

In some embodiments, details of the required scan may be inputted fromanother computer, e.g., through an intranet or through the Internet.Such input may be in addition to, or instead of, input from userinterface 1214.

FIG. 7A is a cross-sectional illustration of a detection head 1112according to some embodiments of the invention. Detection head 1112 hasa breadth B, length L and height H (see FIG. 7B for the length L andheight H). Detection head 1112 may include a detecting unit 1602 in ahousing 1604. For example, the detecting units 1602 may be housed toprotect patient 1110 from swivel motion (illustrated by the arrow 1620)of the detecting unit 1602. Housing 1604 may have a round or curvedcover. In some embodiments, housing 1604 includes a cover shaped with asection 1608 of a cylinder that allows for the swivel of the detectingunit 1602 around a swiveling axis 1610. Detection head 1112 is shown toinclude a parallel hole collimator 1612. Such a collimator may be usedto gain information about the direction from which each photon arrivesat the detection layer 1614. Collimator 1612 may include thin walls 1616(also referred to as septa) that define channels parallel to each other.The walls may be made of materials that have high linear attenuationcoefficient for gamma radiation, such as lead or tungsten. Each photonmay be considered to arrive to a point where it hits detection layer1614 through a channel of the collimator. Most of the photons that hitsepta 1616 are absorbed by the septa, so that mainly photons that gonearly perpendicularly to detection layer 1614 reach the detectionlayer. The near perpendicularity may be expressed as a solid angle, fromwhich the photons have to emerge in order to have a high probability(e.g., larger than 90%) to reach the detection layer. Detecting unit1602 may also include heat sink 1618, which may be attached to thedetection layer on the detection layer side that is free of collimator1612. Detection head 1112 may also include electronics (not shown) fortransferring data to and from the detection layer to processor 1108.

While the explanations above refer to a collimator known in the field asa parallel hole collimator, one or more of collimators 1612 may be of adifferent kind, for example, a pinhole collimator, a slant holecollimator, or a fan beam collimator (e.g., a converging collimator, ora diverging collimator). In some embodiments, different detectors 1112may include collimators of different kinds.

Detection head 1112 may include further parts, as well known in thefield. For example, the detection layer 1614 may include a plurality ofdetection modules, and each may have its own ASIC. The gamma detectormay further include a carrier board which holds all of the detectionmodules, and interfaces to the ASICs. The gamma detector may alsoinclude shielding from external radiation, and additional mechanics tohold the detection layer, ASICs, electronics, cover, etc., together. Thegamma detector may also include a swivel motor, a swivel axis, belt,tensioners, encoder for encoding the exact swivel angle, electronicboards to control the motion of the detector with the gamma detectorand/or inside the gamma detector, and electronic boards to transfer dataindicative of the photons received at the detection layer.

FIG. 7B is a cross-sectional illustration of the detector shown in FIG.7A along a cross-section perpendicular to that depicted in FIG. 7A. FIG.7B illustrates that in some embodiments detector 1112 may be elongated,for example, to almost contact with the patient along a line parallel tothe longitudinal axis of the patient. The length of the detector may besufficient to allow acquiring the entire scan without moving the patient(or the gantry) along the patient, and yet short enough to allow maximalproximity between the detector and the patient taking into account bodycurvatures. A length of about 30 cm to 40 cm is found to be satisfactoryfor imaging grown up humans. FIG. 6B also shows extendable arm 1116. Insome embodiments, the angle between extendable arm 1116 and detector1112 is fixed, e.g., as 90°. In some embodiments, the angle betweenextendable arm 1116 and detector 1112 may be controllable, e.g., byprocessor 1108. In some embodiments, the length of detector 1112 isabout 30 cm, the length of the outer cover is about 40 cm, and theradius of curvature of the round part 1608 of cover 1604 is about 5 cm.The length of the cover may extend beyond the length of the detector,for example, to allow accommodation of electronics, encoders, and/orproximity sensors (all not shown).

Processor 1108 may be configured to determine for each of the multipledetector configurations of the gamma detector a respective weight basedon an absorption profile. The absorption profile may be stored on memory1204 which may make part of processor 1108 or may be accessible toprocessor 1108 in any other way. In some embodiments, the absorptionprofile may be received from outside apparatus 1100 via input 1202. Forexample, input 1202 may allow receiving an absorption profile generatedindependently of apparatus 1100, for example, by a CT scanner or anyother modality, one or more days before scanning by apparatus 1100. Insome embodiments, the absorption profile may be obtained based on aSPECT preview scan made by apparatus 1100, e.g., immediately beforebeginning scanning according to any of the above-mentioned methods. Forexample, the preview scan may be taken using a plurality of detectorconfigurations, allocating a predetermined acquisition time to each ofthem. The predetermined acquisition time may be equal to all thedetector configurations, or acquisition times may be allocated betweenconfigurations according to some heuristic rule, deduced from experiencegained in scanning similar regions of interests in other patients. Insome embodiments, the scanning time devoted to the preview scan may beshort (e.g., 1 minute, 3 minutes, 5 minutes, or any duration longer thanabout 1 minute and shorter than about 10 minutes). Thus, in someembodiments, a user (e.g., a technologist or a physician) first operatesapparatus 1100 to generate a preview scan of the ROI, and indicates toprocessor 1108 (e.g., via a user interface 1212) to use the preview scanfor generating the absorption profile. For example, in some embodiments,the preview scan may be used for determining the outer contour of thebody; and the absorption profile may be assumed to be uniform within theouter contour, for example, as if it was a body of water. In anotherexample, in some embodiments, the preview scan may be matched to a modelof the region of interest obtained offline, for example, a pre-acquiredCT scan. The matching to the preview scan may be used to scale the CTscan, so that an absorption profile generated based on the CT may bescaled and/or oriented to the current dimensions and/or orientation ofthe patient. Dimensions of the region of interest may change, forexample, due to different levels of hydration of the patient.Orientation of the patient may change, for example, if the preview imageand the CT image were taken with the patient at different postures, evenif the difference between the postures is small.

In some embodiments, apparatus 1100 also includes means for obtainingthe absorption profile. For example, apparatus 1100 may include one ormore 3D sensors 1106 configured to provide data indicative ofcoordinates of points on the outer surface of the region to be scanned.Processor 1108 may be configured to generate a model of the outersurface of the ROI based on data received from 3D sensor(s) 1106, forexample, by triangulation. Once a model of the outer surface of the ROIis generated, the absorption profile may be obtained by assuming thatthe volume closed by the outer surface is characterized by a uniformabsorption coefficient, e.g., the absorption coefficient of water in theenergy range of the gamma radiation to be used for the gamma scanning(μ₀). In some embodiments, some portions of the volume may be assumed tobe characterized by absorption coefficient(s) other than that of water,for example, if the ROI includes, at a known position in respect to theouter surface, an air duct (for example, a feeding tube), a metal part(e.g., a prosthesis), or a tissue of known characteristic absorptioncoefficient. Obtaining the absorption profile may include assigning toone or more portions of the ROI absorption coefficient(s), for example,based on one or more of the above assumptions.

In addition to 3D sensor(s) 1106, or instead thereof, apparatus 1100 mayinclude a CT scanner (not shown). The CT scanner may provide a CT scanof the ROI (e.g., of the kind illustrated in FIG. 3A). The CT scannermay provide the absorption profile in a straightforward manner. Forexample, the CT may measure linear attenuation at the X-rays used forthe CT scan, and this may be converted to linear attenuation for gammarays, used for the SPECT.

In addition to 3D sensor(s) 1106, to the CT scanner, or as analternative to one of them or to both, apparatus 1100 may include an MRIscanner (not shown), configured to provide processor 1108 with data,from which the absorption profile may be generated by the processor. Forexample, processor 1108 may be configured to analyze an MRI scan toobtain the absorption profile. In some embodiments, the MRI may be usedto identify locations of different kinds of tissue (e.g., bone, fat,muscles, air, etc.), and assign attenuation coefficients to locationsbased on the kind of tissue identified.

As mentioned above, processor 1108 may be configured to determine foreach of the multiple detector configurations of the gamma detector arespective weight based on the absorption profile. The determination ofthe weights may, in some embodiments, include associating each of aplurality of detector configurations with a visibility value.

Processor 1108 may be further configured to control gamma detector 606to detect gamma radiation from multiple detector configurations based onthe weights determined. For example, in some embodiments, processor 1108may be configured to control the gamma detector to devote more time todetecting gamma radiation when facing the ROI from a direction alongwhich attenuation between the gamma detector and the ROI is higher (orvisibility of the ROI is lower) than to detecting gamma radiation whenfacing the ROI from a direction along which attenuation between thegamma detector and the ROI is lower (or visibility of the ROI ishigher).

In some embodiments, the weights correspond to acquisition durations. Insome embodiments, the processor may be configured to generate a scanningprogram, including all detector configurations to be used, and for howlong gamma radiation is to be detected at each configuration, and thencarries out this scanning program.

For example, in some such embodiments, the processor is configured tobring the gamma detector to a particular detector configuration (e.g.,by controlling movements of an extendible arm on which the gammadetector is mounted); and control the gamma detector to detect gammaradiation for the acquisition duration that corresponds to the weightdetermined for the particular detector configuration. The processor maybe further configured to bring the gamma detector to a newconfiguration, and control the detector to detect gamma radiation at thenew configuration for an acquisition duration that corresponds to theweight determined to the new configuration. This process may continueuntil the detector has detected gamma radiation from multipleconfigurations. In embodiments wherein a scanning program has beengenerated, the above process of bringing to configuration and detectingthere may be carried out according to the scanning plan, until detectiontook place at all planned configurations.

In some embodiments, the weights correspond to sweeping paces, and theprocessor is configured to control the gamma detector to sweepcontinuously among multiple detector configurations at paces based onthe weights. In some such embodiments, the processor is configured tocontrol the gamma detector to sweep continuously among a first pluralityof detector configurations at a first sweeping pace, and sweepcontinuously among a second plurality of detector configurations at asecond sweeping pace. In some embodiments, there may be more than twopluralities of detector configurations, and each may be associated witha respective sweeping pace.

In some embodiments, the weights may correspond to detectorconfiguration density. For example, weights may be determined for somedetector configurations, referred herein as selected detectorconfigurations. In operation, gamma radiation may be detected also inadditional detector configurations, referred herein as non-selectedconfigurations. The non-selected detector configurations may be in thevicinity of the selected one, for example, each selected configurationmay have in its vicinity a number of non-selected configurations. Thisnumber may be determined by the weight. In operation, gamma radiation isdetected from all the configurations, selected and non-selected alike.Assuming configurations that close to each other have similar visibilityvalues, weights corresponding to detector configuration density (i.e.,to the number of non-selected configurations used in the vicinity ofeach selected configuration), make it possible to allocate for eachconfiguration the same acquisition duration, and still allow spendingdifferent acquisition times for detection from configurations withdifferent visibility of the ROI. In some embodiments, the selectedconfigurations may be equally distanced from each other, for example,each may differ from the adjacent one by the same distance, for example,by the same gantry angle difference, and/or by the same swivel angledifference.

Thus, in some embodiments, processor 1108 may be configured to executethe following in respect of each of multiple selected detectorconfigurations:

(a) bring the gamma detector to the selected detector configuration;

(b) control the gamma detector to detect gamma radiation at the selecteddetector configuration;

(c) bring the gamma detector to a non-selected detector configuration,the non-selected detector configuration being in the vicinity of theselected detector configuration;

(d) control the gamma detector to detect gamma radiation at thenon-selected detector configuration; and

(e) repeat (c) and (d) a number of times, each with a differentnon-selected detector configuration in the vicinity of the selecteddetector configuration, said number being dependent on the weightdetermined for the selected detector configuration.

Repeating (a) through (e) for all the selected detector configurationsresults, at least in some selection of detector configurations, to spenddifferent time imaging at configurations of average lower visibilitythan at configurations of average higher visibility even if the timeallocated for each configuration is the same, for example, if thedensity of non-selected configurations differ among different selectedconfigurations.

An exemplary method of scanning according to embodiments of the presentdisclosure includes scanning a region of interest (ROI) by detectinggamma radiation for a first time duration by a first detector that facesthe ROI from a first direction; and for a second time duration by asecond detector that faces the ROI from a second direction. The firstand second detectors may be different detectors or the same detector. Inthe present example, the first duration is longer than the secondduration when attenuation of gamma radiation between the gamma detectorand the ROI is higher along the first direction than along the seconddirection. In other words, the lower is the visibility value of thedetector configuration, the longer is the time spent on scanning at thatconfiguration. This may be achieved based on a predetermined attenuationprofile, based, for example, on a preview scan. However, in someembodiments, the attenuation profile may be generated during the scan,for example, the detector may be controlled to detect radiation from theROI for a given, constant, time period at each configuration, and basedon the radiation detected during this time period decide if to changedetector configuration or to keep detecting radiation for an additionaltime period at this configuration. In some embodiments, the duration ofthe additional time period may be determined based on the amount ofradiation detected during the first time period.

Another exemplary method of scanning may include detecting the gammaradiation while the gamma detector moves among detector configurations;and controlling the movement of the gamma detector to be faster (i.e.higher speed) when attenuation of gamma radiation between the gammadetector and the ROI is low than when attenuation of gamma radiationbetween the gamma detector and the ROI is high.

In some embodiments, the movement of the gamma detector among thedetector configurations is continuous. In some embodiments, the movementmay include bringing the detector to a plurality of distinct detectorconfigurations, and detecting gamma radiation for a predetermined periodwith the detector in each of the distinct radiator configurations, wheredifferent speeds in the preceding example are achieved by havingdifferent densities of detector configurations: the higher thedensity—the slower is the movement. Again, slower movement is devoted todetecting radiations from detector configurations with lower visibilityof the ROI. That is, in some embodiments, the plurality of distinctdetector configurations is arranged with denser detector configurationsin regions where attenuation of gamma radiation between the gammadetector and the ROI is high than when attenuation of gamma radiationbetween the gamma detector and the ROI is low.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art. Forexample, the apparatus described in FIGS. 6A and 6B may be replaced byany other apparatus capable of SPECT imaging by one or more detectorsfrom a plurality of detector configurations, and allows different timeallocations to different detector configurations. In another example,the gamma detector described in FIGS. 7A and 7B may be replaced by anyother gamma detector. Accordingly, it is intended to embrace allalternatives, modifications and variations of parts, methods, systems,or any embodiments described herein, as long as the alternatives,modifications and variations fall within the scope of the appendedclaims.

It is expected that during the life of a patent maturing from thisapplication many relevant methods for scanning a region of interest byone or more gamma detectors will be developed; the scope of the termscanning a region of interest by gamma detector(s) is intended toinclude all such new technologies a priori.

As used herein with reference to quantity or value, the term “about”means “within +10% of”.

The word “exemplary” is used herein to mean “serving as an example”, andnot necessarily as “extremely good”.

The terms “high” and “low” are used to indicate that the “high” ishigher than the “low”. Similarly, the terms “higher” and “lower” areused herein to mean higher than the one referred to as “lower”, andlower than the one referred to “higher”, respectively.

The terms “comprises”, “comprising”, “includes”, “including”, “has”,“having” and their conjugates mean “including but not limited to”.

As used herein, the singular forms “a”, “an” and “the” include pluralreferences unless the context clearly dictates otherwise. For example,the term “a processor” or “at least one processor” may include aplurality of processors, packaged together or separately.

Throughout this application, embodiments of this invention may bepresented with reference to a range format. It should be understood thatthe description in range format is merely for convenience and brevityand should not be construed as an inflexible limitation on the scope ofthe invention. Accordingly, the description of a range should beconsidered to have specifically disclosed all the possible subranges aswell as individual numerical values within that range. For example,description of a range such as “from 1 to 6” should be considered tohave specifically disclosed subranges such as “from 1 to 3”, “from 1 to4”, “from 1 to 5”, “from 2 to 4”, “from 2 to 6”, “from 3 to 6”, etc.; aswell as individual numbers within that range, for example, 1, 2, 3, 4,5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein (for example “10-15”, “10to 15”, or any pair of numbers linked by these another such rangeindication), it is meant to include any number (fractional or integral)within the indicated range limits, including the range limits, unlessthe context clearly dictates otherwise. The phrases“range/ranging/ranges between” a first indicate number and a secondindicate number and “range/ranging/ranges from” a first indicate number“to”, “up to”, “until” or “through” (or another such range-indicatingterm) a second indicate number are used herein interchangeably and aremeant to include the first and second indicated numbers and all thefractional and integral numbers therebetween.

Unless otherwise indicated, numbers used herein and any number rangesbased thereon are approximations within the accuracy of reasonablemeasurement and rounding errors as understood by persons skilled in theart.

It is appreciated that certain features of the invention, which are, forclarity, described in the context of separate embodiments, may also beprovided in combination in a single embodiment. Conversely, variousfeatures of the invention, which are, for brevity, described in thecontext of a single embodiment, may also be provided separately or inany suitable subcombination or as suitable in any other describedembodiment of the invention. Certain features described in the contextof various embodiments are not to be considered essential features ofthose embodiments, unless the embodiment is inoperative without thoseelements.

Although the invention has been described in conjunction with specificembodiments thereof, it is evident that many alternatives, modificationsand variations will be apparent to those skilled in the art.Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and broad scopeof the appended claims.

All publications, patents and patent applications mentioned in thisspecification are herein incorporated in their entirety by referenceinto the specification, to the same extent as if each individualpublication, patent or patent application was specifically andindividually indicated to be incorporated herein by reference. Inaddition, citation or identification of any reference in thisapplication shall not be construed as an admission that such referenceis available as prior art to the present invention. To the extent thatsection headings are used, they should not be construed as necessarilylimiting.

The invention claimed is:
 1. A method of scanning a region of interest(ROI) by at least four gamma detectors, the method comprising:controlling the detectors concertedly to avoid interference between thedetectors, and for each of the detectors; determining, for each ofmultiple detector configurations, a respective weight based on anabsorption profile associating each of a plurality of portions of theROI with a respective gamma attenuation value; and detecting gammaradiation from multiple detector configurations for time periodsallocated among the detector configurations based on the weightsdetermined, wherein the multiple detector configurations comprise aplurality of configuration sets, wherein each configuration set is agroup of configurations that differ only in one respective configurationdescribing parameter.
 2. The method of claim 1, wherein each detectorconfiguration within a configuration set is allocated the same period oftime, and each configuration set is allocated a time corresponding tothe weights.
 3. The method of claim 1, wherein different detectorconfigurations within a configuration set are allocated different periodof times according to the weights.
 4. The method of claim 1, comprisingsweeping continuously among multiple configurations in a configurationset at sweeping speeds corresponding to the weights.
 5. The method ofclaim 1, wherein each detector configuration within a configuration setis allocated the same period of time, and the number of configurationsin the configuration set corresponds to the weights.
 6. The method ofclaim 1, wherein detecting gamma radiation from multiple detectorconfigurations based on the weights determined comprises devoting moretime to detecting gamma radiation with the gamma detector facing the ROIfrom a direction along which attenuation between the gamma detector andthe ROI is higher than to detecting gamma radiation with the gammadetector facing the ROI from a direction along which attenuation betweenthe gamma detector and the ROI is lower.
 7. The method of claim 6,wherein the weights are used to determine movement speeds of thedetectors.
 8. The method of claim 1, comprising using the weights todetermine acquisition durations.
 9. The method of claim 8, comprising,for each of the multiple detector configurations: bringing the gammadetector to the detector configuration; and detecting gamma radiationfor the acquisition duration corresponding to the weight determined forthe detector configuration.
 10. The method of claim 1, wherein theweights are used to determine movement speeds of the detectors.
 11. Themethod of claim 1, wherein the weights are determined based onestimations of total attenuations from points in the ROI to points inthe gamma detector, estimated using the absorption profile.
 12. Anapparatus for scanning a region of interest (ROI), the apparatuscomprising: at least four gamma detectors, each controllable to be atmultiple detector configurations; and a processor configured to:determine for each of the multiple detector configurations of the gammadetector, the detector configurations comprising a plurality ofconfiguration sets, wherein each configuration set is a group ofconfigurations that differ only in one respective configurationdescribing parameter, a respective weight based on an absorptionprofile, the absorption profile comprising an association of each of aplurality of portions of the ROI with a respective gamma attenuationvalue; and control the gamma detector to detect gamma radiation frommultiple detector configurations based on the weights determinedconcertedly to avoid interference between the detectors.
 13. Theapparatus of claim 12, wherein the processor is configured to controlthe gamma detector to devote more time to detecting gamma radiation withthe gamma detector facing the ROI from a direction along whichattenuation between the gamma detector and the ROI is higher than todetecting gamma radiation with the gamma detector facing the ROI from adirection along which attenuation between the gamma detector and the ROIis lower.
 14. The apparatus of claim 12, wherein the weights correspondto acquisition durations, and the processor is configured to execute thefollowing tasks in respect to each of multiple detector configurations:bring the gamma detector to the detector configuration; and control thegamma detector to detect gamma radiation for the acquisition durationcorresponding to the weight determined for the detector configuration.15. The apparatus of claim 12, wherein the weights correspond tosweeping paces, and the processor is configured to control the gammadetector to sweep continuously among multiple detector configurations atpaces based on the weights.
 16. The apparatus of claim 15, wherein theprocessor is configured to control the gamma detector to sweepcontinuously among a first plurality of detector configurations at afirst sweeping pace, and sweep continuously among a second plurality ofdetector configurations at a second sweeping pace.
 17. The apparatus ofclaim 12, wherein the processor is configured to execute the followingin respect of each of multiple selected detector configurations: (a)bring the gamma detector to the selected detector configuration; (b)control the gamma detector to detect gamma radiation at the selecteddetector configuration; (c) bring the gamma detector to a non-selecteddetector configuration, the non-selected detector configuration being inthe vicinity of the selected detector configuration; (d) control thegamma detector to detect gamma radiation at the non-selected detectorconfiguration; and (e) repeat (c) and (d) a number of times, each with adifferent non-selected detector configuration in the vicinity of theselected detector configuration, said number being dependent on theweight determined for the selected detector configuration.
 18. Theapparatus of claim 12, wherein the processor is configured to obtain theabsorption profile from a CT scan.
 19. The apparatus of claim 12,wherein the detector configuration includes position of the gammadetector, orientation of the gamma detector, or both position andorientation of the gamma detector.
 20. The apparatus of claim 12,comprising a gantry, wherein the detector configuration includes agantry angle, and wherein the gamma detector is mounted on an extendablearm supported by the gantry so that the gamma detector can swivel inrespect to the extendable arm, and the detector configuration comprisesa swivel angle of the gamma detector in respect to the extendable arm.